The invention relates to a camera for recording television, photographic or cinematographic images, including a solid-state image sensor in the form of as a charge transfer device comprising a pick-up member, a storage member and a parallel-in, series-out shift register member having at least two shift registers, each being coupled to a distinct sensor output terminal, said storage and shift register members being shielded from incident light and said pick-up member being shielded from incident light over a strip, the image sensor in said camera being operative for obtaining a picture signal having a periodical picture information associated with a scene to be recorded and a periodical dark current information originating from below the said strip and being associated with a signal black level, said picture signal being obtained after a picture information integration period in the pick-up member and a charge transfer period for the transfer between pick-up member and storage member.
A camera of this type, particularly for television, has been described in an English language technical publication no. 150, of the Philips Electronic Components and Materials Division, issued on Jan. 11, 1985, in which the solid-state image sensor is a so-called frame-transfer sensor which is mentioned as an atrractive alternative to the television camera tube. The shift register member has three parallel shift registers which in case of a colour recording based on three primary colours each apply a picture signal corresponding to a given colour to one of the three output terminals. For this purpose construction of the image sensor is availabe with a colour strip filter placed in front of it. Another construction without a colour strip filter is suitable for use in black/white recording or a colour recording with several image sensors. The dark current information originating from below the said shielding strip in the pick-up member occurs in all three picture signals, independent of the construction.
When the described image sensor is used in a black/white or monochrome camera or in a colour camera having more than one image sensor, for example, three, the picture signals originating from the three output shift registers and occuring at the three output terminals of the image sensor are to be combined to one composite camera picture signal. The use of three output shift registers in the image sensor provides the advantage in production that one and the same image sensor construction can be used for both black/white recording and colour recording with one image sensor, apart from the additional provision of the colour strip filter. In addition there is the advantage of the higher pixel density in the television line scan i.e. the horizontal direction than in the case of the use of a single output shift register. In fact, the limited minimum width of the control electrodes in the image sensor imposes a limit on the minimum horizontal distance between charge packets in the image sensor and this distance is reduced by a factor of three when three shift registers are used.
With the two advantages described there is the problem in monochrome camera or the colour camera having several image sensors that the contributions of the picture signals originating from each of the three output shift registers to the composite camera picture signal should be equally large. Scene pixels having the same information content must occur in the camera picture signal with more or less the same signal value between black level and peak white level. In practice especially differences between the black levels in the three picture signals originating from the shift registers are found to be inadmissible so that no balanced composite picture signal can result without any further measures. Upon display of such an unbalanced composite picture signal a troublesome interference pattern of vertical stripes if found to occur.